Projectin assembly and interactions during myofibril formation. A.J. Ayme-Southgate , R.J. Southgate , T. Love , S.E. Richardson. Biology, College of Charleston, Charleston, SC.

   The muscle protein projectin is an extremely large protein (~1 MgDa) with a modular repeated structure. Projectin localizes over the A band region of the myofibril in synchronous muscles. Projectin's temporal expression and assembly, during embryonic muscle formation, will be presented and compared to other major sarcomeric proteins. Studies were performed both on embryo squashes and on primary myoblast cultures. The early assembly of projectin and in particular the comparison with myosin heavy chain assembly is consistent with projectin's proposed role as a scaffold in myofilament formation. Various regions of projectin, expressed as fusion proteins, were used in in vitro binding assays to determine projectin's interactions with other sarcomeric proteins. Data from these assays, in particular the myosin/projectin binding will be discussed in the context of the formation of the sarcomeric structure. The effects of mutations in projectin and myosin heavy chain upon myofibrillogenesis will be presented.